Method and means for reducing crosstalk in carrier-current signaling systems



June 10, 1930. 5 BLACK 1,762,755

H- 7 METHOD AND MEANS FOR REDUCING CROSSTALK IN CARRIER CURRENT SIGNALING SYSTEMS Filed May 31, 1928 2 Sheets-Sheet l fiaZ Z Z 2: ll .3 .3 .3 J 3 .3 .3 3 E fie. 0"

June 10, 1930. H. 5. BLACK I 1,7 2,7 5

METHOD AND MEANS FOR-REDUCING CROSSTALK IN CARRIER CURRENT SIGNALING SYSTEIIS Filed May 31, 1928 2 Sheets-Sheet. 2

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(7x314 C v I //V V5 N 70/? Y #129040 5 Eula/r ITTOFIWEY l i I HAROLD S. BLAGK, OI IONTULAIB, NEW JERSEY, ASSIGNOB .l'O BELL Patented June 10,

UNITED STATES PATENT oFFic mnmmn LABORATORIES, INCORPORATED, OF NEW YORK, 1i. Y-, A CORPORATE)! O] m YORK Inrnon in ms ron 'animcme 'cnossnnx m c SYSTEMS Application filed Kay 31,

This invention relates to methods and means for reducing cross-talk between signaling systems.

An object of the invention is to reduce crosstalk between paralleling signaling systems.

The invention provides a simple and efli- .cient arrangement for reducing crosstalk between paralleling signaling systems which operates to maintain the currents transmitted in the same direction in each system at substantially the same energy level at all -points where the transmission lines run parallel and adjacent to each other.

When two ,or more signaling systems are operated on the same pole line or in the same cable, one of the principal problems encountered is to reduce crosstalk or mutual interaction due to the inductive or capacity eflects between adjacent systems.

In order to prevent crosstalk in voice frequency signaling systems, it is customary to transpose the pairs of wires at intervals which are short relative to the wave lengths of the currents employed. This is practicablein such systems since the frequencies are relatively low and the wave lengths correspondingly long. In carrier current signaling systems, however, where the wave lengths involved are relatively short, transpositions are required at much more frequent intervals and the problem of reducing crosstalk becomes increasingly diflicult.

It has been found, as described .in my Patent No. 1,676,627, issued July 10, 1928,

that crosstalk can be reduced by maintaining lowering the energy level ofthe other line by a resistance pad at the transmitter, compensation being effected at the receivers by a ad and amplifier respectively. However, w en the adjacent lines are not ofthe same gauge wire, or otherwise differ in transmission characteristics, considerable crosstalk will be produced es cially at the higher frequencies due to t e di'fierent attenuation characteristics of the lines.

I be re erred 1928. Serial no. 281,898.

According to a feature of the present invention when paralleling carrier transmission systems use conductors for one line which are not of the same gauge as the conductors used on the, other line, carrier line transfer connections are employed at intervals between the limits within which the lines parallel each other to transfer the car-- srcmimo rier currents from the system operated over the smaller gauge line to the larger gauge line and to transfer the carrier currents from thelarger gauge line to the smaller. Since in multiplex systems, the carrier frequency terminus and the voice frequency terminus are in many cases not the-same, it is desirable to have the voicecurrents continuously transmitted over the same line and low pass filters can be employed for this purpose.

According to another feature oi the present invention, when the paralleling carrier transmission systems employ conductors having different attenuation characteristics and over which relatively high carrier frequenciesare transmitted orwhere there are a plurality of adjacent parallel systems, nonamplifying auxiliary devices having attenuationcharacteristics which vary with the frequency are employed at'intervals between the limits within which the lines parallel each other so that the resultant transmission level of said auxiliary system and the Line in which they are used is substantially the same over the range of frequencies trans-' mitted as that of the other lines.

The invention will be described in connection with its application to single channel carrier current telephone systems, but it will be evident that it is also applicable to other types of signaling systems.

Referring to the drawings Fig. 1 shows two adjacent transmission lines employing conductors having difl'erent attenuation characteristicsto which the invention is applicable.

Fig. 2shows one method of reduc ngthe crosstalk between the lines shown 1n F 1g. 1 in accordance with the invention.

Fi 3 is a detailed drawing which will to later in connection with 2.

Fig. 4 shows another method of reducing the crosstalk between the lines shown in Fig. 1 in accordance with the invention.

Fig. 5' is a detailed drawing which will be referred to later in connection with Fig. 4.

Referring to Fig. 1, W and E designate two distant stations between which there are two two-way carrier transmission systems employing bands of frequencies for transmission in the same direction over each line. The transmission lines are located on the same pole line or in the same cable. One of thesystems employs a line L, the conductors of which are of a lar er gauge wire than the conductors of line 2 employed in the other system. The two-way systems may be of the types disclosed in U. S. Patent 1,602,019, issued Octobe 15,. 1926 to C. L. Weis, J r., or in my Pate t 1,653,837, issued December 27, 1927. Two-way repeaters A are located at intervals in lines L and L These repeaters may be of the type disclosed in U. S. Patent 1,413,357 issued to P. A. Raibourn, April 18, 1922;.

Assume that we transmit east on both lines, starting from the west terminal W at a transmission level of +15 TU with a frequency of 27 KC, that at this frequency the loss of a 250 mile span of the No. 8 gauge wire line is 40 TU, and the loss of the No. 12 gauge line is 56 TU, then the transmission level at the east end of the s an will be -25 TU for the No. 8 gauge no and 41 TU for the No. 12 gauge line. This is a 16 TU level difference between the lines at this point. By transmission level is meant the strength of the signal current, expiessed in transmission units (TU) above or below the arbitrary standard. Since the two lines have different attenuation characteristics, the only point along the two lines at'which the transmission level is equal is at the starting point.

At the other points along the lines the slgnaling levels on the 8 gauge line will be above those onthe 12 auge line and on account of this level difierence the crosstalk introduced into the 12 gauge line from the Segauge line will be more predominant than that introduced into the 8. gauge line from 10,512 gauge line when the currents are amplified' at a-repeat'er or terminal station to the desired level. This crosstalk is reduced in one form of the invention by causing the signaling currents retpresenting one message to traverse one line or part of the distance and the other line for the rest of the distance. Suitable circuit connections for accomplishing this are illustrated in Figs. 2

and 3 to whichreference will now be made.

' Referring to Fig. 2, carrier line transfer filters 3 may be located at intervals in lines L and L of the transmission system shown in Fig. land are composed entirely of fil-' ters. These filters are employed to transfer the carrier currents from the system oper- These filters, HF and HF,, are arranged to transmit the desired carrier frequencies, while substantiall suppressing all other frequencies. In or erto transmit the voice fre uencies over their respective lines L an L, and to suppress the carrier fre uencies from continuing along lines L and filters LR and L13 are located in lines L and Labetween the connections to filters HF and. HF Filters LF and LF, .are' designed to substantially suppress carrier frequencies which it is desired to transfer from line L, to L and from L to line L while freely transmitting such frequencies as it is desired to transmit along lines L and L The filters in'the arrangements just described may be of any desired character, the only requirement being that they shall transmit the desired ranges of frequencies to the substantial exclusion of other frequencies. Preferably these filters should be of the general type disclosed in U. S. patents to G. A. Campbell 1,227,113 and 1,227,114, dated May 22, 1917.

It will be seen from the drawing that the carrier currents are transferred at intervals from one line to the other, so that the resultant paths for the currents transmitted over the two, systems have substantially the same attenuation characteristics and there- .fore the resultant energy level at any point along the line will be substantially the same for currents transmitted inthe same direction over both systems and the resultant crosstalk becomes substantially as small as where paralleling systems employ conduc-' tors of the same gauge wire.

Instead of transferring each message from one line to the other at intervals in order to provide paths which-have substantially the same overall attenu ion, loss may be introduced at intervals i the higher level line in accordance with a second form of the invention, to reduce crosstalk between the lines. The circuit connections and a paratus for these will now be to Fi s. 4; and 5. O Re erring to Fig. 4,.crosstalk attenuators 5 may be located at intervals in'the line L; of the transmission-system shown in Fig, 1 so that the resultant transmission loss of H line L and the attenuators issubstantially described re erring ploy is shown diagrammatically in Fig. 5.

The voice frequency currents are transmitted freely along the line L through the lowpass filter LP, while the carrier currents are substantially. suppressed by this filter. The

7 carrier currents from west to east are transmitted from the line L, through high-pass filters (land 7, eastward attenuators 10 to 13, high-pass filters 8 and 9 .to line L,. The

filter 9, low-pass filter 14, westward attenuators 10 to 13, low-pass filter and high- 7 pass filter 6 to the line L The attenuators 10 to 13 are designed so that the individual attenuators will attenuate for different len ths of line and may represent, for examp e, spans of 12 25, 50 and 75 mile lengths respectively. Those not needed for any given length may be omitted or effectively shunted out by shortcircuiting the connections. Where a single installation is made in a 150 mile an, 50 miles east of the west terminal, all ut the 50 mile unit will be shunted out in the east-' ward attenuator and the 12% and 50 mile units will be shunted. out in the westward attenuators. The attenuator units 10 to 13 amaybe of the type disclosed in U. S. Pat- I cut 1,591,073, issued July 6, 1926 to O. J.

Zobel, having a constant resistance characteristic impedance suitable for terminating the carrier circuits.

The amount of crosstalk between the two lines will depend upon the number of attenuator units 5 installed in any given span.

conditions the attenuation of a 250 mile s an of No. 8 gauge wire will be 40 TU w ile the attenuation of the No. 12 gauge line will be 56 TU. If an attenuator 5 is placed mid-way between the west and east terminals and is so designed that the attenuation of the No. 8 gauge line plus the attenuation of the equalizer is equal to the attenuation of the No. 12 gauge line at the output of the attenuator 5, the transmission levels on both lines at this point will then be the same and the transmission level at the east this point but to bring the level of the 'No..

8 gauge line to a point below the level of the No. 12 gauge line such that the level difference will be zero at a point mid-way minal, the level difference at the end of the line will then be the same as the level difference at theoutputof the equalizer and the crosstalk from the No. 8 gauge line L to the No. 12 gauge line L, will be still further reduced. It is apparent, however, that this condition will increase the crosstalk from the No. 12 gauge line L to the No. 8 gauge line L since for a portion of the length of the span the transmission level of the No. 12 gauge line L will be greater than that of the No. 8 gauge line L The level difference between the two lines may be still further decreased by reducing the transmission level of the output at the west terminal on the No. 8 gauge line L so that the level difference between thelines becomes zero at a point mid-way between the west terminal and the attenuator centrally located. This may be accomplished by actually reducing the output level or by the use of an attenuator. The latter method is preferable for the attenuator may be designed to attenuate the different frequencies transmitted so that all frequencies will have the zero level difference at the desired point. This attenuator, located at the'output of the terminal or amplifier, would have loss characteristics which are one-half those of the adjacent attenuator.

Additional crosstalk. attenuators 5 located half way between the terminals of the line and the crosstalk attenuator 5 centrallv located will reduce the-,resultant crosstalk to in the number of crosstalk attenuators 5 will still further reduce the crosstalk be For example, as stated above, under certain tween the two lines.' The number of units to be employed in any given system will depend upon the maximum allowable amount of crosstalk.

The invention is also capable of use for reducing the crosstalk where the lines having different gauge Wire parallel each other for only part of their length. In such case the use of attenuators such as disclosed in Fig. 5 need be used only between the limits within which said lines parallel each other. The transmission level" of the two lines at the point of intersection can be adjusted to the desired level either by locating an attenuator at the junction of said lines or at the sending terminal or amplifier to provide the desired level at the point of intersection.

The invention is also capable of other modifications and adaptations not specifically referred to, but included within the scope of the appended claims.

Although specific examples have been referred to in the specification in order to make the invention clear, it is understood that the references .to a given length of span, to the No. 8 and No. 12 gauge lines, and to a frequency of 27 KC or to other numerical values are to be taken as illustrative and not in any way limiting the invention.

For the purposes of this specification the transmission equivalent of a line refers to the difference in transmission levels betwee the two ends of the line.

What is claimed is:

1. A signal transmission.- system comprising adjacent lines paralleling each other and having different transmission characteristics, terminal stations therefor, and means intermediate said terminal stations for providing two transmission paths over said lines of substantially the same transmission equivalent between the extreme limits wlthin which said lines parallel each other, said means comprising a plurality of frequency discriminating attenuating elements inserted between adjacent carrierxcurrent signalingin the line having the higher transmission level.

2.-The method of reducing the crosstalk systems having different transmission characteristics, which comprises introduc'n loss elements at frequent intervals in oneio said systems between the extreme limits i which said lines parallel each other and maintaining the transmission characteristics of both systems substantially the same between said limits.

3. The method of reducing the crosstalk between adjacent carrier current signaling systems, which comprises attenuating the currents in one of said systems at frequent intervals between the extreme limits within which said systems parallel each other to maintain substantially the same transmission equivalent in both systems at the frequencies J transmitted between said limits,-'and thereby maintain the currents transmitted in the same direction in both systems at substanti ally'the same energy level.

4; In a transmission system, a pair of par allel adjacent transmission lines, the respective attenuations of which vary with frequency, said transmission lines havin different transmission characteristlcs, a p urahty of auxiliary systems in one of said lines intermediate the terminal stations of said vtransmission system, said auxiliary systems having attenuation characteristics which vary with the frequency in a manner such that the resultant transmission of said auxiliary systemand said last mentioned line is substantially the same over the range of frequencies transmitted as that of the other of said lines. i 5. The combination with a plurality of carrier current signalings'ystems having adjacent transmission lines of respectively different transmission characteristics, employing substantially the same 'directionalbands of carrier frequencies, of frequency dlscrlminating means associated with at least one of said lines tomaintainthe currents transmitted in one direction thereover at substantially the same energy level in the respective lines.

x 6. The combination with a pair of carrier I current signaling systems having adjacent transmission lines of different transmission characteristics, employing substantially the same directional bands of carrier frequencies, of frequency discriminating attenuating means associated with one of said systems to maintain the currents transmitted i rality of auxiliary systems inserted in at least one of said lines at points intermediate said repeaters and intermediate the terminal stations and the repeatersadjacent to said termmal vstations, said auxiliary systems having attenuation characteristics which varywlth the frequency in a manner such that the resiiltant transmission equivalent of said auxiliary system and said lines is substantially the same for both of said lines.

8. In a transmission system, two geographically separated stations, 1 terminating lines at said stations, a pair-of transmission paths interconnecting said stations, both paths bein used for transmission in one direction 0 substantially the same bands of carrier frequencies, said paths having different transmission characteristics, auxiliary systems inserted in the path having the higher transmission level and so ,designed and proportioned as to maintain the resultant transmission characteristics of said pathhaving the higher transmission level and the auxiliary s stems associated therewith substantially t e same as the transmission characteristics of the other of said paths between the extreme in whichsaid paths parallel each other.

9. In a signalling system a plurality of transmission lines, terminal stations therefor, *means for simultaneously transmitting over said lines in one direction signals havm certain of said hnes having transmission a ing substantially the same carrier frequency,

characteristics which differ from the characteristics of the others of said lines, repeating apparatus in each of said lines for ampllfying the currents transmitted, and frequency discriminating means associated with said certain lines at intervals between said individual repeating stations and between said terminal stations and the adjacent re- I peating station for maintaining the combined transmission characteristics of said certain lines and the frequency discriminating means associated therewith substantially the same as that of the others of said lines between the extreme limits in which said lines parallel each other.

10. The combination with a pair of carrier current signaling systems comprising terminal transmitting and receiving circuits and employing substantially the same frequencies in the respective transmitting circuits, of transmission lines which are adjacent each other for at least a portion of their length and which have respectively different transmission characteristics, and attentuation equalizers associated with at least one of said transmission lines to maintain the currents transmitted in one direction thereover at substantially the same energy level in both of said'signaling systems between the extreme limits within which said transmission lines parallel each other.

11. The method of reducing crosstalk between carrier current signaling systems employing substantially the same frequencies in the respective transmittin circuits and having transmission lines w ich are adjacent each other for only a limited portion of their length and which have substantially different transmission characteristics, which comprises reducing the energy level of the currents at the transmitting terminal as-' sociated with one of said lines to substantially the same value as the currents at a oint intermediate the terminals of an adacent transmission line, maintaining said currents along the res ective lines at substantially thesame' va ue between the extreme limits in which said systems parallel each other, and amplifying the currents received at the distant terminal of said first mentioned tr nsmission line to compensate for the red ction in ener level at the transmitting terminal thereo 12. In a multi-channel carrier signaling system, employing a plurality of paralleling l nes having different frequency-attenuation characteristics, and over ,which lines carrier currents having the same frequency are transmitted in the same direction, the

method of substantially equalizing the attenuation of said parallehng lines at the frequencies transmitted in the same direction which comprises reducing the energy level ofthe carrier currents transmitted over the lines having the higher transmission level at periodic intervals between repeater -stations and between the terminals and the adjacent-repeater stations to substantially the same transmissionlevel as the other lines.

13. In a multi-channel carrier signaling i system, employi a plurality of paralleling lines having fierent frequency-attenuation characteristics,and over which lines cent repeaters to provide substantially the.

same transmission level as the other lines.

14. In a multi-channel carrier signaling system, employing a plurality of paralleling lines having different frequency-attenuation characteristics, and over which lines carrier currents having the same frequencies are transmitted in the same direction, terminal stations and amplifier stations associated with said lines, means for substantially equalizing the attenuation of said paralleling lines at the frequencies transmitted in the. a e direction, said means comprising frequency discriminating devices associated with said lines having the higher transmission levels at equal intervals between said amplifier stations and between said terminal stations and the adjacent amplifier stations to provide substantially the same transmission levelas the other lines, and attenuation equalizers located at the sending end of said terminal stations and said amplifier stations, having Iloss characteristics which are one-half those of the adjacent non-amplifying devices at all frequencies transmitted.

day of May, 1928.

my name this 29th HAROLD S. BLACK. 

